Download a. The Sampling Method

C. SURVEY METHODS
a.
The Sampling Method
The sampling, estimation, and investigation methods used in the Labour Force Surveys have
changed since the survey first began in 1954. The methods described in this chapter are
those that have been in place since 2012.
As of the beginning of 2012, the Labour Force Survey has also been changed from a
quarterly format to a monthly format. Data are collected every month from about 21,300
persons aged 15 and over on an ongoing basis.
For explanations about the methods used in the Labour Force Surveys until 2011 (inclusive)
see the publication Labour Force Surveys 2011.1
The changes in the survey methods, definitions and questionnaire which were made in
1954–2003 were gathered into a special technical publication.2
The sample drawn each year is allocated to 12 mutually exclusive and complementary
groups, known as panels. The panels are introduced into the survey investigation in 12
consecutive months, where one panel a month is introduced in the calendar year following
the year in which the sample is drawn.
Each panel is investigated eight times according to a pattern known as 4-8-4. In the
rotational structure of this pattern, eight investigations are performed for each panel in the
following way: the investigation in the introduction month and in the three following months
(investigations 1-4), a break of eight months, and four more consecutive investigations in the
following months (investigations 5-8). This pattern was chosen based on various uses of the
survey estimates, because it reduces sampling errors of the estimates of changes between
two consecutive months and two consecutive years.
Each year contains 27 exclusive panels from three different sampling years.
Each following two year period includes 15 shared panels and 12 exclusive panels.
Most of the final sampling units are dwellings, which are sampled in two stages. In the first
stage, localities are sampled, with probability proportional to size. In the second stage,
dwellings are sampled in the sampled localities, so that the final sampling probability of the
dwelling is equivalent to the sampling fraction of that year.
The sample of localities in the survey is taken from a list of localities (the locality sampling
frame), and the localities are placed in four main groups, by the size of the locality, as
determined by the estimates of number of persons aged 15 and over.
1
Central Bureau of Statistics (2012). Labour Force Surveys 2011. Publication No. 1504. Jerusalem:
Author, Introduction to Chapter B.
2
Central Bureau of Statistics (2006). Labour Force Survey: Changes in the Methodology, Definitions
and Questionnaire 1954–2003. Technical Publication No. 78. Jerusalem: Author.
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In the first three groups, all localities are included with certainty every year:
a. Large localities that are included in all 12 new panels of that year’s sample. Each year this
group includes the 40 largest localities in the country, and covers about 64% of the
persons aged 15 and over in the population.
b. Other large localities which are smaller than those in Group A above are included in at
least one panel (but not in every panel) every month of the year. In that way, every month
there is at least one interviewing portion of dwellings in each locality. Each year, about 50
localities of this type are sampled, covering about 18% of the persons aged 15 and over in
the population.
c. Smaller localities included in only one or two panels a year. Thus, each locality is
represented only in some months of the year. Each year about 30 localities of this type
are sampled, covering about 4% of the persons aged 15 and over in the population.
d. "Probability" localities – small urban localities and all rural localities – are sampled
randomly from the list of localities, so that the probability of a locality being sampled is
proportional to its size. Each year a sample of localities is drawn, which is dependent on
the previous year’s sample. This ensures that many different localities are included in the
samples of two adjacent years. Altogether, each year about 200 “probability” localities are
sampled from about 1,000 localities in the sampling frame, covering about 14% of the
persons aged 15 and over in the country. The sample in each locality is usually placed in
one panel.
In every locality that is sampled, a sample of residential dwellings is taken, although
sometimes (mostly in non-urban localities) households or other units are sampled.
A small portion of the current sample is derived through other methods, due to their suitability
to the sample frame and other constraints, and is not derived through the main method
described above. Examples are: samples of student dormitories and immigrant absorption
centers, which are not covered in the sample frame of localities, and the sample of new
building additions that represent the population entering dwellings whose construction was
completed after the sampling process. For a detailed explanation on the sampling and on
special samplings, see the CBS publication Labour Force Surveys 2012.1
Every month, over 9,000 households participate in the survey, so that over 100,000
interviews of households are conducted during the survey year. Notably, the vast majority of
households are interviewed several times (up to four interviews) in a given year. In 2012,
over 35,000 different households were interviewed, of which about 17,000 households were
interviewed in four different months.
1
Central Bureau of Statistics (2015). Labour Force Surveys 2012. Publication No. 1565. Jerusalem:
Author, Introduction, "methods".
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b.
The Estimation Method
The data collected in the survey are subject to quality control and cleaning procedures (in the
Data Editing and Processing System). The process includes about 250 different logical
checks to identify logical errors in the collected data.
The data collected in the survey relate to the sample. To transform the data into estimates for
the entire population, a “weighting coefficient” is allocated to each individual in the sample, and
all of the data for the sample are multiplied by the weighting coefficient. Using the weighting
coefficients, estimates are calculated for the monthly sample. The annual estimates presented
in this publication are arithmetical averages of the 12 monthly estimates.
The estimation method is intended to reduce both sampling errors and bias that may occur
because the characteristics of the households that participated in the survey may differ from
those that did not participate.
In the monthly Labour Force Survey, a new estimation method was introduced. The new
method, known as Regression Composite Estimation, was proposed by Fuller and Rao
(2001). In the composite estimates, data on individuals and households surveyed in a given
month are calibrated in terms of the total known population of cross-sections by geographic
area, sex and age group, in the same way that calibration was done in the quarterly Labour
Force Survey. However, in contrast to the quarterly Labour Force Survey, the composite
method also calibrates data on labour force characteristics based on estimates from the
previous month.
The method also ensures synchronization of the characteristics of individuals and the
characteristics of the households they belong to through the use of an identical weighting
coefficient for each person in the same household. The weighting coefficient reflects both the
number of households and the number of persons in the population represented by the
given household.
The set of weighting coefficients is determined by an iterative process that yields full
compatibility between the weighted distributions of persons and the current demographic
estimates of the Central Bureau of Statistics, based on the last Census and on the changes
made after the Census, according to weighting groups.1
The division into weighting groups is independent of religion, by geographic groupings and
by population characteristics (age*sex), as seen in Table C/5, in the CBS publication Labour
Force Surveys 2012.2
In 2012, a number of changes were made in the definitions of the weighting groups, following
changes in the distribution of the population.
1
2
For details, see Central Bureau of Statistics (2010). Labour Force Surveys 2009. Publication No.
1417. Jerusalem: Author. Introduction, Chapter E.
Central Bureau of Statistics (2015). Labour Force Surveys 2012. Publication No. 1565. Jerusalem:
Author. Introduction, "Methods".
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